Ultrasonic diagnostic apparatus and control method thereof

ABSTRACT

An ultrasonic diagnostic apparatus includes a probe including a transducer which transmits an ultrasound signal to a target, receives the ultrasound signal reflected from the target, and transduces the received ultrasound signal into an analog signal; an A/D converter which converts the analog signal output by the probe into a digital signal; a compression unit which compresses the digital signal output from the A/D converter; and a host computer which decompresses the digital signal compressed by the compression unit and performs beamforming.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/205,972, filed Aug. 9, 2011, which claims priority from Korean PatentApplication No. 10-2010-0076649, filed Aug. 9, 2010 in the KoreanIntellectual Property Office, the entire disclosures of which areincorporated herein by reference.

BACKGROUND

1. Field

Apparatuses and methods consistent with embodiments relate to anultrasonic diagnostic apparatus to create a two or three-dimensionalimage of an internal shape of a target and a control method thereof.

2. Description of the Related Art

An ultrasonic diagnostic apparatus transmits ultrasound to a target tobe tested and receives the ultrasound signal reflected from the target.The ultrasonic diagnostic apparatus converts the received ultrasoundsignal into an electrical image signal to display an internal state ofthe target. The ultrasound signal is transmitted and received through aprobe. The probe includes a transducer to transduce an electrical signalinto a transmitting ultrasound signal, and to transduce the ultrasoundsignal reflected from the target into an electrical image signal. Aplurality of transducers arranged in various forms may be used toimprove resolution.

Referring to FIG. 1, which shows an example of a probe including aplurality of transducers 10, ultrasound signals transmitted from therespective transducers 10 are set to be simultaneously focused upon afocus point located at a depth d. The distance between a centertransducer Tc and the focus point is the shortest, and the distancebetween an end transducer Tn and the focus point is the longest. Arelated art ultrasonic diagnostic apparatus includes a transmissionbeamformer to generate a plurality of transmission signals in view ofdifferences in the distances between the focus point and the respectivetransducers 10. The transmission beamformer generates a plurality ofelectrical transmission signals, i.e., transmission beams, based on adelay profile which takes into account the differences in the distancesbetween the respective transducers and the focus point. The transmissionbeams are transmitted to the respective transducers 10. The transducers10 transduce the transmission beams into ultrasound signals, which aretransmitted to the focus point.

The times needed for the ultrasound signals reflected from the focuspoint to reach the respective transducers 10 are different. Anultrasound reflection signal directed to the center transducer Tctravels a distance r. On the other hand, an ultrasound signal reaching atransducer Tx distant from the center transducer Tc by a distance x hasa time delay corresponding to a difference Δr in the distance betweenthe transducers Tx and Tc and the focus point. The beamformercompensates for the delay in receiving the signals at the respectivetransducers based on the position of the center transducer Tc.

SUMMARY

Exemplary embodiments provide an ultrasonic diagnostic apparatus thatperforms a beamforming operation using software, and a control methodthereof.

In accordance with an aspect of an exemplary embodiment, there isprovided an ultrasonic diagnostic apparatus including a probe includingat least one transducer to transmit an ultrasound signal to a target,receive an ultrasound signal reflected from the target, and transducethe received ultrasound signal into an analog signal, ananalog-to-digital (A/D) converter to convert the analog signal outputfrom the probe into a digital signal, a compression unit to compress thedigital signal output from the A/D converter, and a host computer todecompress the digital signal compressed by the compression unit and toperform beamforming.

The compression unit may predict a target pixel of the digital signalfrom an ambient pixel to generate a prediction error signal, and codethe prediction error signal to perform compression.

The compression unit may generate the prediction error signal bycalculating the prediction error signal using horizontal(channel-direction) data, vertical (depth-direction) data, andvector-direction (time-direction) data of the digital signal.

The compression unit may generate the prediction error signal using thehorizontal (channel-direction) data, the vertical (depth-direction)data, and the vector-direction (time-direction) data of the digitalsignal by applying a higher weight factor to the vertical direction andthe vector-direction data than the horizontal data to generate aprediction signal and calculating a difference between a pixel value ofthe prediction signal and a pixel value of a real signal to generate theprediction error signal.

The compression unit may code the prediction error signal to performcompression by creating a compressed code word from a sequence of theprediction error signal and coding the compressed code word.

The compression unit may remove spatial redundancy, temporal redundancyand statistical redundancy from the digital signal to performcompression.

The host computer may perform beamforming to create a frame data signal,and perform digital signal processing on the frame data signal to createultrasonic image data.

The host computer may convert the ultrasonic image data into image framedata having a scan line display format.

The ultrasonic diagnostic apparatus may further include a display unitto receive and display the image frame data.

In accordance with an aspect of another exemplary embodiment, there isprovided a method of controlling an ultrasonic diagnostic apparatus, themethod including compressing an ultrasound signal reflected from atarget, and transmitting the compressed signal to a host computer whichdecompresses compressed signal and performs beaming forming.

Compressing the ultrasound signal may include predicting a target pixelof the ultrasound signal from an ambient pixel to generate a predictionerror signal and coding the prediction error signal to performcompression.

Predicting the target pixel of the ultrasound signal from the ambientpixel to generate the prediction error signal may include generating theprediction error signal based on a horizontal variation, a verticalvariation, and a time-direction variation of the ultrasound signal.

Generating the prediction error signal based on the horizontalvariation, the vertical variation, and the time-direction variation ofthe ultrasound signal may include applying a higher weight factor to thevertical variation and the time-direction variation than the horizontalvariation to calculate a prediction signal and determining a differencebetween a pixel value of the prediction signal and a pixel value of areal signal to generate the prediction error signal.

Coding the prediction error signal to perform compression may includecreating a compressed code word from a sequence of the prediction errorsignal and coding the compressed code word.

The control method may further include removing spatial redundancy,temporal redundancy and statistical redundancy from the ultrasoundsignal to perform compression.

In accordance with an aspect of another exemplary embodiment, there isprovided a method of controlling an ultrasonic diagnostic apparatus, themethod including compressing an ultrasound signal reflected from atarget, converting the ultrasound signal into a digital signal,predicting a target pixel of the digital signal from an ambient pixel togenerate a prediction error signal, coding the prediction error signalto perform compression, and performing beamforming using a host computerwhen the compressed data is transmitted to the host computer.

Predicting the target pixel of the digital signal from the ambient pixelto calculate the prediction error signal may include calculating theprediction error signal based on horizontal (channel-direction) data,vertical (depth-direction) data, and vector-direction (time-direction)data of the digital signal.

Generating the prediction error signal using the horizontal(channel-direction) data, the vertical (depth-direction) data, and thevector-direction (time-direction) data of the digital signal may includeapplying a higher weight factor to the vertical direction and thevector-direction data than the horizontal data to generate a predictionsignal and generating a difference between a pixel value of theprediction signal and a pixel value of a real signal.

Coding the prediction error signal to perform compression may includecreating a compressed code word from a sequence of the prediction errorsignal to code the compressed code word and performing compression.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become apparent and more readilyappreciated from the following description of exemplary embodiments,taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic view illustrating an ultrasound signaltransmission and reception focusing method using a transducer array;

FIG. 2 is a functional block diagram of an ultrasonic diagnosticapparatus, according to an exemplary embodiment;

FIG. 3 is a detailed block diagram of a compression unit included in theultrasonic diagnostic apparatus, according to an exemplary embodiment;

FIG. 4 is a block diagram illustrating a context-based, adaptive,lossless image coding (CALIC) compression method;

FIG. 5 is a view illustrating a method of calculating a prediction errorof an ultrasound signal using a CALIC prediction method, according toone exemplary embodiment; and

FIG. 6 is a schematic view illustrating a time-based arrangement of aplurality of vectors on an image acquired from an ultrasound signal,according to one exemplary embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings, wherein likereference numerals refer to like elements throughout.

FIG. 2 is a function block diagram of an ultrasonic diagnostic apparatus200 according to an exemplary embodiment.

The ultrasonic diagnostic apparatus 200 includes a probe 100, ananalog-to-digital (A/D) converter 110, a compression unit 120, a hostcomputer 130, and a display unit 140.

The probe 100 includes at least one transducer (not shown) to transducean electrical signal into an ultrasound signal and transmit theultrasound signal to a target. The at least one transducer may alsoreceive the ultrasound signal reflected from the target and transducethe ultrasound signal into an electrical signal (analog signal). Theanalog signal output from the probe 100 has a center frequency relatedto properties of the transducer and tissues.

The A/D converter 110 converts the analog signal output from the probe100 into a digital signal by sampling the analog signal at a fixedsampling rate of, for example, 60 MHz. The A/D converter 110 performssampling at such a fixed sampling rate irrespective of the size of thecenter frequency of the analog signal. When the center frequency of theanalog signal is low, therefore, a relatively large amount of digitalsignals is acquired. When the center frequency of the analog signal ishigh, on the other hand, a relatively small amount of digital signals isobtained. When the probe 100 includes a plurality of transducers, aplurality of A/D converters 110 corresponding to the respectivetransducers is provided.

The compression unit 120 compresses the digital signal output from theA/D converter 110. Upon reception of the digital signal output from theA/D converter 110, the compression unit 120 compresses the digitalsignal.

The compression unit 120 may use a lossless compression process tocompress the digital signal. The lossless compression process compressesthe digital signal such that when the compressed data is restored, therestored data completely coincide with data before compression.

The compression unit 120 may use context-based, adaptive, lossless imagecoding (CALIC), or Lossless JPEG from the Joint Photographic ExpertsGroup (JPEG-LS) as the lossless compression technology.

The CALIC compression method is described in detail in X. Wu and N.Memon, “Context-based, adaptive, lossless image coding,” IEEETransactions on Communications, Vol. 45, No. 4, April 1997, pp. 437-444,the disclosure of which is incorporated herein.

The JPEG-LS compression method is described in detail, for example, in“Lossless and non-lossless coding of continuous tone still images,”ISO/IEC JTC1/SC29 WG1 14495, the disclosure of which is incorporatedherein.

The CALIC and JPEG-LS compression methods use differential pulse codemodulation (DPCM). Each pixel of a picture is scanned every line andevery row. DPCM predicts a target pixel from an ambient pixel to code aprediction error signal thereof. DPCM losslessly encodes originalinformation.

That is, upon lossless compression, a prediction error signal iscalculated based on a value of an ambient pixel around each pixel. Anentropy encoder encodes the calculated prediction error signal of thepixel value, i.e., the difference between an effective value and thepixel value of the prediction signal. The lossless compression methodsused in exemplary embodiments are not limited to CALIC and JPEG-LS.Other known lossless compression methods may be used. In addition, lossycompression methods may also be used. Since exemplary embodiments areapplied to medical imaging, lossless compression methods may beprimarily used. One of the lossless compression methods, CALIC, will bedescribed in detail with reference to FIGS. 3 to 5.

The host computer 130 decodes the data transmitted from the compressionunit 120 to decompress the data, and performs a beamforming operationusing software to create frame data signals, which are raw data.Beamforming is a process in which some of the digital signals areprocessed at a rate corresponding to an integer multiple of the centerfrequency to form a reception beam. The host computer 130 converts thedigital signals output from the compression unit 120 into apredetermined number of frame data signals.

The host computer 130 digital signal processes the frame data signals toform ultrasonic image data that express a B, C or D mode.

The host computer 130 converts the ultrasonic image data into apredetermined scan line display format, which is a data format used inthe display unit 140. That is, the host computer 130 converts theultrasonic image data signals into image frame data that is displayed inthe display unit 140.

The host computer can be a processor unit. The processor unit can be aCPU, GPU and Computer.

The display unit 140 receives the image frame data to display anultrasound image.

The communication of data of two of the probe 100, an A/D converter 110,a compression unit 120, host computer 130 and the display unit 140, maybe performed using one of a cable and a wireless network.

FIG. 3 is a detailed block diagram of the compression unit included inthe ultrasonic diagnostic apparatus according to an exemplaryembodiment, and FIG. 4 is a block diagram illustrating a context-based,adaptive, lossless image coding (CALIC) compression method.

The compression unit 120 includes a picture buffer 121, a pixel sequencegenerator 122, a predictor 123, an adder 124, and an entropy encoder125.

The image buffer 121 accumulates a picture input from an externalapparatus. The pixel sequence generator 122 scans the pictureaccumulated in the picture buffer 121 to extract an ambient pixel from acurrent pixel, i.e., a target pixel. For each pixel, the pixel sequencegenerator 122 supplies a pixel value of the current pixel to the adder124 and also supplies a pixel value of the ambient pixel to thepredictor 123.

The predictor 123 creates a prediction signal based on the pixel valueof the ambient pixel supplied from the pixel sequence generator 122 andsupplies the prediction signal to the adder 124. The adder 124 subtractsthe prediction signal supplied from the predictor 123 from the pixelvalue of the current pixel supplied from the pixel sequence generator122 to obtain a prediction error signal and supplies the predictionerror signal to the entropy encoder 125.

The entropy encoder 125 creates and outputs a compressed code word froma sequence of the prediction error signal supplied from the adder 124.

The prediction error signal is coded into a prefix having a variablelength and a suffix having a fixed length. The prefix having thevariable length is a series of “0” bits following “1” bits. The sequenceof the prediction error signal is partitioned into blocks. For eachblock, an optimum length of the suffix is decided first. The code wordis transmitted before the code word is coupled to the prediction errorsignal of each block. The entropy encoder 125 is described in detail,for example, in R. Rice, “Lossless coding standards of space datasystems,” IEEE 1997, the disclosure of which is incorporated herein.

The above-described coding method is divided into prediction and entropycoding, as shown in FIG. 4. CALIC prediction will be described in detailwith reference to FIG. 5. CALIC entropy coding uses Huffman coding andarithmetic coding, which are conventional coding methods.

The Huffman coding is a form of entropy coding which is used in losslesscompression. The Huffman coding is an algorithm using codes havingdifferent lengths according to the estimated probability of occurrenceof specific data segments. Upon coding of different letters, Huffmancoding does not use a fixed number of bits but uses statisticaldistribution. Therefore, Huffman coding is a coding method using asmaller number of bits with respect to a frequently appearing value anda larger number of bits with respect to an infrequently appearing value.

Arithmetic coding is a form of entropy coding which is used in losslesscompression. Arithmetic coding estimates a probability of an inputsignal from a frequency of occurrence of the input signal. In otherforms of entropy coding, each symbol is replaced with a code in aone-to-one correspondence. In arithmetic coding, on the other hand, anentire message is replaced with a single real number n.

The Huffman coding and the arithmetic coding are conventionaltechnologies, and therefore, a detailed description thereof is notnecessary.

FIG. 5 is a view illustrating a method of calculating a prediction errorof an ultrasound signal using a CALIC prediction method.

An ultrasound signal reflected from a target exhibits a spatialredundancy having similarity in axial and azimuth directions. Also, theultrasound signal has a statistical redundancy in which a predictionerror is increased in proportion to a horizontal variation or achannel-direction variation dh and a vertical variation or adepth-direction variation dv (see FIG. 6 in connection with thehorizontal and vertical variations).

The CALIC compression method predicts a pixel value usinggradient-adjusted prediction (GAP) to obtain a prediction error e, whichis the difference between a predicted value Î and a real value I. Thehorizontal variation dh, the vertical horizontal variation dv, thepredicted value Î, and the real value I may be obtained using thefollowing equation:Î=GAP(&dh,&dv)dh=abs(I(w)−I(ww))+abs(I(n)−I(nw))+abs(I(ne)−I(n))dv=abs(I(w)−I(nw))+abs(I(n)−I(nn))+abs(I(ne)−I(nne))e=I−Î

I(w) is a pixel value of a point located at w of FIG. 5, I(ne) is apixel value of a point located at ne of FIG. 5, and abs( ) is anabsolute value of a value in parentheses.

The ultrasound signal reflected from the target exhibits highersimilarity in the axial direction than in the azimuth direction.Therefore, to obtain the prediction error, a higher weight factor isapplied to the vertical variation or the depth-direction variation dvthan to horizontal variation or a channel-direction variation dh.

In compression, data is predicted and the difference between thepredicted value and the real value are coded. For this reason, aparameter may be adjusted based on the properties of ultrasonic radiofrequency (RF) data, and an algorithm may be changed to increase acompression rate. When viewing the property of the ultrasonic diagnosticapparatus 200, therefore, the reflected ultrasound signal forms atemporal redundancy. Referring to FIG. 6, the ultrasound signal includesa plurality of vectors, which are obtained with time delay. RF dataobtained with time delay has similar temporal redundancies, which may beused in prediction.

Upon calculation of the prediction error using CALIC, a time-directionvariation or a vector-direction variation dp is included as a parameter,and, upon obtaining the predicted pixel value, an algorithm is changedto include de (or dprev). The changed equation is as follows:Î=GAP(&dh,&dv,&dprev)dh=abs(I(w)−I(ww))+abs(I(n)−I(nw))+abs(I(ne)−I(n))dv=abs(I(w)−I(nw))+abs(I(n)−I(nn))+abs(I(ne)−I(nne))dp=abs(I(w)−I(wp))+abs(I(n)−I(np))+abs(I(ne)−I(nep))

Upon obtaining the gradient-adjusted prediction (GAP) from the aboveequation, a weight factor is applied to dv higher is higher than aweight factor applied to dh, since RF data exhibit higher similarity inthe axial direction than in the azimuth direction. Also, a weight factoris applied to dv is higher than a weight factor applied to dh, since RFdata has high temporal redundancy.

FIG. 6 shows a horizontal (channel-direction) data variation directiona-b, a vertical (depth-direction) data variation direction a-c, and avector-direction (time-direction) data variation direction a-d.

As is apparent from the above description, the beamforming operation isperformed by the host computer 130 using software rather than hardware,thereby reducing manufacturing costs of the ultrasonic diagnosticapparatus.

Also, an ultrasound signal is compressed and transmitted to the hostcomputer, thereby increasing a transmission rate and thus rapidlyperforming a post-processing operation on the ultrasound signal.

Although a few exemplary embodiments have been shown and described, itwill be appreciated by those skilled in the art that changes may be madein these exemplary embodiments without departing from the principles andspirit of the inventive concept, the scope of which is defined in theclaims and their equivalents.

What is claimed is:
 1. An ultrasonic diagnostic apparatus comprising: aprobe comprising at least one transducer which transmits an ultrasoundsignal to a target, receives the ultrasound signal reflected from thetarget, and transduces the received ultrasound signal into an electricalsignal; and a compressor which compresses the electrical signal bypredicting a target pixel of the ultrasound signal from an ambient pixelto generate a prediction error signal and coding the prediction errorsignal, wherein the signal compressed by the compressor is decompressedwhen the signal is used for beamforming.
 2. The ultrasonic diagnosticapparatus according to claim 1, wherein the compressor generates theprediction error signal using at least one of channel-direction data anddepth-direction of the electrical signal.
 3. The ultrasonic diagnosticapparatus according to claim 2, wherein the compressor generates theprediction error signal using the at least one of the channel-directiondata and the depth-direction data of the electrical signal by applyingweight factors to the at least one of the channel-direction data and thedepth-direction to generate a prediction signal and determining adifference between a pixel value of the prediction signal and a pixelvalue of a real signal, and wherein the weight factor applied to thedepth-direction is higher than the weight factor applied to thechannel-direction data.
 4. The ultrasonic diagnostic apparatus accordingto claim 1, wherein the compressor codes the prediction error signal bycreating a compressed code word from a sequence of the prediction errorsignal and coding the compressed code word.
 5. The ultrasonic diagnosticapparatus according to claim 1, wherein the compressor removes spatialredundancy, temporal redundancy and statistical redundancy from theelectrical signal to compress the electrical signal.
 6. The ultrasonicdiagnostic apparatus according to claim 1, wherein the signal compressedby the compressor is beamformed so that a frame data signal is created,and the frame data signal is processed so that an ultrasonic image datais created.
 7. The ultrasonic diagnostic apparatus according to claim 6,wherein the ultrasonic image data is converted into image frame datahaving a scan line display format.
 8. The ultrasonic diagnosticapparatus according to claim 7, further comprising a display unit whichreceives the image frame data from the host computer and displays theimage frame data.
 9. A method of controlling an ultrasonic diagnosticapparatus, the method comprising: compressing an ultrasound signalreflected from a target by predicting a target pixel of the ultrasoundsignal from an ambient pixel to generate a prediction error signal, andcoding the prediction error signal; transmitting the compressedultrasound signal to a decompressor; and decompressing the compressedsignal and performing beaming forming.
 10. The method according to claim9, wherein the predicting the target pixel of the ultrasound signal fromthe ambient pixel to generate the prediction error signal comprisesgenerating the prediction error signal based on at least one of achannel-direction variation and a depth-direction variation.
 11. Themethod according to claim 10, wherein the generating the predictionerror signal comprises applying weight factors to the at least one of achannel-direction variation and the depth-direction variation togenerate a prediction signal and determining a difference between apixel value of the prediction signal and a pixel value of a real signal,and wherein the weight factor applied to the depth-direction variationis higher than the weight factor applied to the channel-directionvariation.
 12. The method according to claim 9, wherein the coding theprediction error signal to perform compression comprises creating acompressed code word from a sequence of the prediction error signal andcoding the compressed code word.
 13. The method according to claim 9,wherein the compressing the ultrasound signal comprises removing spatialredundancy, temporal redundancy and statistical redundancy from theultrasound signal.
 14. A method of controlling an ultrasonic diagnosticapparatus, the method comprising: compressing an ultrasound signalreflected from a target; predicting a target pixel of the ultrasoundsignal based on an ambient pixel to generate a prediction error signal;coding the prediction error signal to generate compressed data;transmitting the compressed data to a decompressor; and decompressingthe compressed data and beamforming using a decompressed data.
 15. Themethod according to claim 14, wherein the predicting the target pixelcomprises generating the prediction error signal based on at least oneof a channel-direction data and depth-direction.
 16. The methodaccording to claim 15, wherein the generating the prediction errorsignal comprises: applying weight factors to the channel-direction dataand the depth-direction data; and calculating the prediction errorsignal comprises calculating a difference between a pixel value of theprediction signal and a pixel value of a real signal, wherein the weightfactor applied to the depth-direction data is higher than the weightfactor applied to the channel-direction data.
 17. The method accordingto claim 14, wherein the coding the prediction error signal comprisescreating a compressed code word from a sequence of the prediction errorsignal to code the compressed code word and performing compression.